I have done some work on this, suggestions, feedback (and help ) would be nice....
1) My project is here: https://github.com/espenmn/medialog.markdown
2) You need to install it from the control panel
3) it adds a behavior, markdown behavior. Add a new content type and add this behavior to it
4) It adds some control panel settings, where one can set 'extra buttons' (you will need to add datagridfield JS )
5) Add a new 'My content type', New buttons will be to the right of 'Preview'
6) The preview button will show your markdown before it is saved (not sure if it renders it 100% correct)
7) Extra buttons are set in the control panel
8) The text you set in the control panel will be added:
9) On save the 'admonition extensions' will show ( https://pythonhosted.org/Markdown/extensions/admonition.html ), if you have enabled this for markdown.
I could need some help on how to get the markdown extensions to preview correctly. DONE
Could there be a way to 'read it through portal transform' ? YES
Off course, a 'live preview' like https://community.plone.org would be great .... Works, but turned off since it would be too slow (?)
- It would also be nice if the bodyText field used this editor when set to markdown instead of html.
I have had troubles with using the Richtext field, because the rich text behavior always defaults to html (evn if set in control panel to something else). and adding a Richtext field TTW gives errors on save (instead of saving the input, it saves 'did you mean Raw or output)